Processing of melt processible liquid crystal polymer by control of thermal history

Abstract

A process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics is provided. The process comprises the steps of subjecting the liquid crystal polymer to an elevated temperature between the DSC transition temperature and the degradation temperature of the polymer; cooling the liquid crystal polymer to a processing temperature which is between the DSC transition temperature and the elevated temperature and at which the liquid crystal polymer is less subject to degradation than at the elevated temperature; and extruding the liquid crystal polymer into the form of a shaped article having mechanical properties which are improved over those of articles formed from liquid crystal polymer which has not been subjected to the elevated temperature. Preferably, the liquid crystal polymer exhibits at the elevated temperature a reduction by at least a factor of 5 in the melt viscosity of the liquid crystal polymer, as compared to the melt viscosity at the DSC transition temperature, without significant degradation of the liquid crystal polymer. The reduction in melt viscosity is substantially retained by the liquid crystal polymer at the processing temperature, and the liquid crystal polymer is extruded into the form of a shaped article while the reduction in melt viscosity is thus retained. By employing the process of the present invention, melt processable liquid crystal polymers can be conveniently processed at temperatures near the DSC transition temperature rather than at the higher temperatures commonly encountered in the prior art at which degradation is more likely to occur.

We claim: 
     
       1. A process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics, said process comprising the steps of: (a) subjecting said liquid crystal polymer to an elevated temperature between the differential scanning calorimetry transition temperature and the degradation temperature of the polymer;   (b) cooling said liquid crystal polymer to a processing temperature which is between said differential scanning calorimetry transition temperature and said elevated temperature and at which said liquid crystal polymer is less subject to degradation than at said elevated temperature; and   (c) extruding said liquid crystal polymer into the form of a shaped article having mechanical properties which are improved over those of articles formed from liquid crystal polymer which has not been subjected to said elevated temperature.   
     
     
       2. The process of claim 1 wherein said elevated temperature is within the range of approximately 40° C. to 100° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer. 
     
     
       3. The process of claim 1 wherein said liquid crystal polymer is subjected to said elevated temperature for a period of time not greater than approximately five minutes. 
     
     
       4. The process of claim 1 wherein said elevated temperature and said period of time are sufficient to effect a reduction by at least a factor of 5 in the melt viscosity of said liquid crystal polymer, as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       5. The process of claim 1 wherein said liquid crystal polymer comprises wholly aromatic polyester which is capable of forming an anisotropic melt phase. 
     
     
       6. The process of claim 5 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature of at least approximately 275° C. 
     
     
       7. The process of claim 1 wherein said liquid crystal polymer is extruded through a die to form a film. 
     
     
       8. The process of claim 1 wherein said liquid crystal polymer is extruded through a spinneret to form filaments. 
     
     
       9. The process of claim 1 wherein said liquid crystal polymer is extrusion molded to form a molded article. 
     
     
       10. A process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics and which yields shaped articles having improved properties, said process comprising the steps of: (a) subjecting said liquid crystal polymer to an elevated temperature between the differential scanning calorimetry transition temperature and the degradation temperature of the polymer for a period of time, wherein said elevated temperature and said period of time are sufficient to effect a reduction by at least a factor of 5 in the melt viscosity of said liquid crystal polymer, as compared to the melt viscosity at said differential scanning calorimetry transition temperature, without significant degradation of said liquid crystal polymer;   (b) cooling said liquid crystal polymer to a processing temperature which is between said differential scanning calorimetry transition temperature and said elevated temperature and at which said liquid crystal polymer substantially retains the melt viscosity exhibited by said liquid crystal polymer at said elevated temperature and at which said liquid crystal polymer is less subject to degradation, the melt viscosity of said liquid crystal polymer at said processing temperature after exposure to said elevated temperature being substantially less than the melt viscosity of said liquid crystal polymer at said processing temperature without having been exposed to said elevated temperature; and   (c) extruding said liquid crystal polymer into the form of a shaped article while the melt of said liquid crystal polymer substantially retains the melt viscosity exhibited by said liquid crystal polymer at said elevated temperature.   
     
     
       11. The process of claim 10 wherein said elevated temperature is within the range of approximately 40° C. to 100° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer. 
     
     
       12. The process of claim 10 wherein said liquid crystal polymer is subjected to said elevated temperature for a period of time not greater than approximately five minutes. 
     
     
       13. The process of claim 10 wherein said elevated temperature and said period of time are sufficient to effect a reduction by at least a factor of 10 in the melt viscosity of said liquid crystal polymer, as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       14. The process of claim 13 wherein said elevated temperature and said period of time are sufficient to effect a reduction by at least a factor of 100 in the melt viscosity of said liquid crystal polymer, as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       15. The process of claim 14 wherein said elevated temperature and said period of time are sufficient to effect a reduction by at least a factor of 1,000 in the melt viscosity of said liquid crystal polymer as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       16. The process of claim 10 wherein said liquid crystal polymer comprises wholly aromatic polyester which is capable of forming an anisotropic melt phase. 
     
     
       17. The process of claim 16 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature of at least approximately 275° C. 
     
     
       18. The process of claim 10 wherein said liquid crystal polymer is extruded through a die to form a film. 
     
     
       19. The process of claim 10 wherein said liquid crystal polymer is extruded through a spinneret to form filaments. 
     
     
       20. The process of claim 10 wherein said liquid crystal polymer is extrusion molded to form a molded article. 
     
     
       21. A process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics and which yields shaped articles having improved properties, said process comprising the steps of: (a) subjecting said liquid crystal polymer for a period of time not greater than approximately five minutes to an elevated temperature within the range of approximately 40° C. to 100° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer, thereby effecting a reduction by at least a factor of 5 in the melt viscosity of said liquid crystal polymer, as compared to the melt viscosity at said differential scanning calorimetry transition temperature, without significant degradation of said liquid crystal polymer;   (b) cooling said liquid crystal polymer to a processing temperature within the range of approximately 5° C. to 40° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer, wherein said processing temperature is at least approximately 15° C. less than said elevated temperature; and   (c) extruding said liquid crystal polymer into the form of a shaped article while the melt of said liquid crystal polymer substantially retains the melt viscosity exhibited by said liquid crystal polymer at said elevated temperature.   
     
     
       22. The process of claim 21 wherein said liquid crystal polymer is subjected to an elevated temperature of approximately 60° C. to 85° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer. 
     
     
       23. The process of claim 22 wherein said liquid crystal polymer is subjected to an elevated temperature of approximately 85° C. above the differential scanning calorimetry transition temperature of said liquid crystal polymer. 
     
     
       24. The process of claim 21 wherein said liquid crystal polymer is subjected to said elevated temperature for a period of time of approximately 0.5 to 60 seconds. 
     
     
       25. The process of claim 24 wherein said liquid crystal polymer is subjected to said elevated temperature for approximately 30 seconds. 
     
     
       26. The process of claim 21 wherein said reduction in the melt viscosity of said liquid crystal polymer is a reduction by at least a factor of 10 as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       27. The process of claim 26 wherein said reduction in the melt viscosity of said liquid crystal polymer is a reduction by at least a factor of 100 as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       28. The process of claim 27 wherein said reduction in the melt viscosity of said liquid crystal polymer is a reduction by at least a factor of 1,000 as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       29. The process of claim 21 wherein said liquid crystal polymer comprises wholly aromatic polyester which is capable of forming an anisotropic melt phase. 
     
     
       30. The process of claim 29 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature of at least approximately 275° C. 
     
     
       31. The process of claim 30 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature within the range of approximately 300° C. to 350° C. 
     
     
       32. The process of claim 29 wherein said wholly aromatic polyester comprises a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 350° C. consisting essentially of the recurring moieties I and II wherein: ##STR3## wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, and approximately 10 to 90 mole percent of moiety II. 
     
     
       33. The process of claim 29 wherein said wholly aromatic polyester comprises a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 325° C. consisting essentially of the recurring moieties I, II, and III wherein: ##STR4## wherein said polyester comprises approximately 30 to 70 mole percent of moiety I. 
     
     
       34. The process of claim 21 wherein said liquid crystal polymer is extruded through a die to form a film. 
     
     
       35. The process of claim 21 wherein said liquid crystal polymer is extruded through a spinneret to form filaments. 
     
     
       36. The process of claim 21 wherein said liquid crystal polymer is extrusion molded to form a molded article. 
     
     
       37. A process for the extrusion of melt processable wholly aromatic polyester capable of forming an anisotropic melt phase which provides improved processability characteristics and which yields shaped articles having improved properties, wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature of at least approximately 275° C., said process comprising the steps of: (a) subjecting said wholly aromatic polyester for a period of time of approximately 0.5 to 60 seconds to an elevated temperature within the range of approximately 60° C. to 85° C. above the differential scanning calorimetry transition temperature of said wholly aromatic polyester, thereby effecting a reduction by at least a factor of 10 in the melt viscosity of said wholly aromatic polyester, as compared to the melt viscosity at said differential scanning calorimetry transition temperature, without significant degradation of said wholly aromatic polyester;   (b) cooling said wholy aromatic polyester to a processing temperature within the range of approximately 5° C. to 40° C. above the differential scanning calorimetry transition temperature of said wholly aromatic polyester; and   (c) extruding said wholly aromatic polyester into the form of a shaped article while the melt of said wholly aromatic polyester substantially retains the melt viscosity exhibited by said wholly aromatic polyester at said elevated temperature.   
     
     
       38. The process of claim 37 wherein said wholly aromatic polyester is subjected to an elevated temperature of approximately 85° C. above the differential scanning calorimetry transition temperature of said wholly aromatic polyester. 
     
     
       39. The process of claim 37 wherein said wholly aromatic polyester is subjected to said elevated temperature for approximately 30 seconds. 
     
     
       40. The process of claim 37 wherein said reduction in the melt viscosity of said liquid crystal polymer is a reduction by at least a factor of 100 as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       41. The process of claim 40 wherein said reduction in the melt viscosity of said liquid crystal polymer is a reduction by at least a factor of 1,000 as compared to the melt viscosity at said differential scanning calorimetry transition temperature. 
     
     
       42. The process of claim 37 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature within the range of approximately 300° C. to 350° C. 
     
     
       43. The process of claim 37 wherein said wholly aromatic polyester comprises a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 350° C. consisting essentially of the recurring moieties I and II wherein: ##STR5## wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, and approximately 10 to 90 mole percent of moiety II. 
     
     
       44. The process of claim 37 wherein said wholly aromatic polyester comprises a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 325° C. consisting essentially of the recurring moieties I, II and III wherein: ##STR6## wherein said polyester comprises approximately 30 to 70 mole percent of moiety I. 
     
     
       45. The process of claim 37 wherein said liquid crystal polymer is extruded through a die to form a film. 
     
     
       46. The process of claim 37 wherein said liquid crystal polymer is extruded through a spinneret to form filaments. 
     
     
       47. The process of claim 37 wherein said liquid crystal polymer is extrusion molded to form a molded article. 
     
     
       48. A process for the extrusion of melt processable wholly aromatic polyester capable of forming an anisotropic melt phase which provides improved processability characteristics and which yields shaped articles having improved properties, wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature of at least approximately 275° C. and is selected from the group consisting of: (i) a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 350° C. consisting essentially of the recurring moieties I and II wherein: ##STR7## wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, and approximately 10 to 90 mole percent of moiety II, and   (ii) a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temperature below approximately 325° C. consisting essentially of the recurring moieties I, II, and III wherein: ##STR8## wherein said polyester comprises approximately 30 to 70 mole percent of moiety I, said process comprising the steps of:     (a) subjecting said wholly aromatic polyester for a period of time of approximately 0.5 to 60 seconds to an elevated temperature of approximately 85° C. above the differential scanning calorimetry transition temperature of said wholly aromatic polyester, thereby effecting a reduction by at least a factor of 10 in the melt viscosity of said wholly aromatic polyester, as compared to the melt viscosity at said differential scanning calorimetry transition temperature, without significant degradation of said wholly aromatic polyester;   (b) cooling said wholly aromatic polyester to a temperature within the range of approximately 5° C. to 40° C. above the differential scanning calorimetry transition temperature of said wholly aromatic polyester; and   (c) extruding said wholly aromatic polyester into the form of a shaped article while the melt of said wholly aromatic polyester substantially retains the melt viscosity exhibited by said wholly aromatic polyester at said elevated temperature.   
     
     
       49. The process of claim 48 wherein said wholly aromatic polyester is subjected to said elevated temperature for approximately 30 seconds. 
     
     
       50. The process of claim 48 wherein said wholly aromatic polyester exhibits a differential scanning calorimetry transition temperature within the range of approximately 300° C. to 350° C. 
     
     
       51. The process of claim 48 wherein said wholly aromatic polyester is extruded through a die to form a film. 
     
     
       52. The process of claim 48 wherein said wholly aromatic polymer is extruded through a spinneret to form filaments. 
     
     
       53. The process of claim 48 wherein said wholly aromatic polyester is extrusion molded to form a molded article.